INTERANNUAL TO INTERDECADAL VARIATIONS OF THE REGIONALIZED SURFACE CLIMATE OF THE UNITED STATES AND RELATIONSHIPS TO GENERALIZED FLOW PARAMETERS

This analysis attempts to discern primary causes of interannual and interdecadal climate variations for precipitation and temperature regions of the conterminous United States. Varimax rotated principal components analysis of annual climate division data is used in the derivation of nine precipitation and five temperature regions. Each region's time series is examined for underlying linear trends, representing long-term climate change, and tests for variance changes, to determine regional climate variability shifts. The first six precipitation components, representing the entire eastern half of the country and the Northwest, displayed significant temporal increases. Of these, four displayed significant increases in interannual variability through time. For temperature, only the Southwestern region showed a significant change (increase) through time. However, significant reductions in temperature variability were confirmed for three regions. To determine the causes of the derived climate shifts, correlation analysis was performed with various atmospheric teleconnection indices. Precipitation trends are most strongly associated with variations in the Southern Oscillation Index (SOI) at the interannual time scale while interdecadal variations are associated more with variations in the Pacific/North American (PNA) teleconnection. Both interannual and interdecadal variations of regional temperature are most strongly related to the PNA, except for the Southwest, which showed a significant correlation to the SOI. This suggests that El Niño/Southern Oscillation (ENSO) events are the source for much of the precipitation change evident in the eastern and Northwestern United States and temperature change in the Southwest. [Key words: climate change, precipitation, temperature, El Niño, Southern Oscillation, United States climate.]     

Numerical experiments on dynamic stiffening of beams and plates

By introducing continuous or discontinuous variations in the thickness of beams, arches and plates, it is possible in many practical situations to raise the value of the fundamental frequency and, at the same time, to lower the weight of the structural element. This is a beneficial situation, especially in those cases where weight reduction and large dynamic stiffness are of interest. The present paper surveys some recent practical accomplishments in this area.The rigorous procedure consists, from a general structural optimization viewpoint, of minimizing an objective function (for instance, total volume) subject to constraints on the geometry and behavior (natural frequencies, buckling loads, etc.). In many instances it is convenient to reverse the problem: one fixes or limits the weight or volume and constructs some quantity which describes the desired behavior of the system e.g. the fundamental frequency.The problems under study in the present paper are considerably more modest in scope, since the procedure is performed by numerical experiments.     

Parametric identification of solar series based on an adaptive parallel methodology

In this work we present an adaptive parallel methodology to optimize the identification of time series through parametric models, applying it to the case of sunspot series. We employ high precision computation of system identification algorithms, and use recursive least squares processing and ARMAX (Autoregressive Moving Average Extensive) parametric modelling. This methodology could be very useful when the high precision mathematical modelling of dynamic complex systems is required. After explaining the proposed heuristics and the tuning of its parameters, we show the results we have found for several solar series using different implementations. Thus, we demonstrate how the result precision improves.     

Construction of a high-resolution gridded rainfall dataset for Peru from 1981 to the present day

ABSTRACT

A new gridded rainfall dataset available for Peru is introduced, called PISCOp V2.1 (Peruvian Interpolated data of SENAMHI’s Climatological and Hydrological Observations). PISCOp has been developed for the period 1981 to the present, with an average latency of eight weeks at 0.1° spatial resolution. The merging algorithm is based on geostatistical and deterministic interpolation methods including three different rainfall sources: (i) the national quality-controlled and infilled raingauge dataset, (ii) radar-gauge merged precipitation climatologies and (iii) the Climate Hazards Group Infrared Precipitation (CHIRP) estimates. The validation results suggest that precipitation estimates are acceptable showing the highest performance for the Pacific coast and the western flank of the Andes. Furthermore, a meticulous quality-control and gap-infilling procedure allowed us to reduce the formation of inhomogeneities (non-climatic breaks). The dataset is publicly available at https://piscoprec.github.io/ and is intended to support hydrological studies and water management practices.     

Glacial Cirques in the Southern Side of the Cantabrian Mountains of Southwestern Europe

A total of 156 glacial cirques located on two different areas in the Cantabrian Mountains (NW Spain) were identified and measured in order to continue and expand the study of these large‐scale erosional forms in European mountains. Environmental variables that may explain cirque distribution (altitude, aspect and lithology), and their most important morphometric features (area, length (L), width (W), headwall height (H), and L/W, L/H and W/H indices), are analysed. Statistical analysis has been applied as indicators of contrast (ANOVA) and association (correlation and regression). Conglomerate analysis (CLUSTER) has been used to discriminate cirque groups based on their morphometric variables. Results show that cirques occur at lower altitudes in the Upper Sil River basin area than in the Montaña Central area due to a lower former equilibrium line altitude (ELA) position. In the Upper Sil River basin, environmental variables appear to have had a strong influence on the location and size of cirques: the largest cirques are located in quartzite rocks at elevations above 2000 m and face N or NE. In Montaña Central, the influence of these factors was more limited as a consequence of higher geological structure control. Cirque sizes generally are modest compared with cirques present in other mountain ranges globally, most likely due to shorter glacial occupancy in the Cantabrian Mountains.     

Evaluation of redox-sensitive metals in marine surface sediments influenced by the oxygen minimum zone of the Humboldt Current System,Northern Chile

Upwelling coastal systems can be used to understand how dissolved oxygen and biological productivity control the accumulation of redox-sensitive metals in marine sediments. The aluminium (Al), cadmium (Cd), iron (Fe), nickel (Ni), molybdenum (Mo), vanadium (V), total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS) contents in surficial sediment collected from different water depths (30, 70, and 120?m) in three northern Chilean bays influenced by coastal upwelling and oxygen minimum zones (OMZs) were measured. Principal component analysis (PCA), cluster analysis, and Spearman?s rank correlation were used to identify the mechanisms responsible for the redox-sensitive metal accumulation. The content of redox-sensitive metals and organic components in sediment increased with increasing water column depth, whereas lithogenic metals decreased. In the Mejillones del Sur and Caldera bays, the enrichment factors of the redox-sensitive metals showed enrichment for all metals with depth. The Cd and V enrichments are mainly the product of biogenic flow to the seabed, and the Mo and Ni enrichments are due to preservation under low subsurface oxygen conditions. Sulfate reduction is not an important mechanism in the accumulation of redox-sensitive metals in the sediment of the three bays. The PCA showed that the behaviors of the redox-sensitive metals and organic components reflect differences in the effects of the OMZ in sediment along the coast of northern Chile, with a more intense OMZ in Mejillones del Sur bay and weaker OMZs in Caldera and Inglesa bays. However, the high degree of enrichment in redox-sensitive metals in Caldera Bay can be attributed to the intense activity of the mining industry near the bay, a situation that produces geochemical behavior similar to that observed in Mejillones del Sur Bay.     

The CaT strength in Seyfert nuclei revisited: analysing young stars and non-stellar light contributions to the spectra

In a former paper, we have presented spectra of 64 active, nine normal and five starburst galaxies in the region around the near-infrared calcium triplet (CaT) absorption lines and the [S  iii ]λ9069 line. In the present paper, we analyse the CaT strength ( W _CaT) and kinematical products derived in that study, namely stellar  (σ_★)  and ionized gas (σ_gas) velocity dispersions. Our main results may be summarized as follows. (1) Type 2 Seyfert galaxies show no sign of dilution in W _CaT with respect to the values spanned by normal galaxies, even when optical absorption lines such as the Ca  ii K band at 3933 Å are much weaker than in old, bulge-like stellar populations. (2) The location of type 2 Seyfert galaxies in the   W _CaT– W _CaK  plane is consistent with evolutionary synthesis models. The implication is that the source responsible for the dilution of optical lines in these active galactic nuclei (AGN) is a young stellar population, rather than an AGN featureless continuum, confirming the conclusion of the pioneer study of Terlevich, Díaz & Terlevich. (3) In type 1 Seyfert galaxies, both   W _{[S  iii ]}  and W _CaT tend to be diluted due to the presence of a non-stellar component, in agreement with the unification paradigm. (4) A comparison of  σ_★  with σ_gas (obtained from the core of the [S  iii ] emitting line) confirms the existence of a correlation between the typical velocities of stars and clouds of the narrow line region. The strength and scatter around this correlation are similar to those previously obtained from the [O  iii ]λ5007 linewidth.